Glutamate antagonists in rat hippocampus.

1 Hippocampal cellular responses to acidic amino acids and some of their antagonists were measured in the rat anaesthetized with urethane. The effects of these antagonists of the field responses of the rat hippocampus to afferent stimulation were measured in acute as well as chronically prepared rats. 2. Hippocampal pyramidal cells were excited by microiontophoretic application of glutamate and aspartate. These responses were antagonized by glutamic acid diethyl ester (GDEE), glutamic acid dimethyl ester (GDME) and by proline. Partial specificity could be seen as excitatory responses to acetylcholine were less susceptible to the antagonists. 3 field responses of the hippocampus to commissural stimulation were reduced significantly in both an acutely prepared or the conscious rat following parenteral administration of GDEE and GDME but not proline. Responses to perforant path stimulation were not affected by these drugs. 4 It is suggested that an acidic amino acid may serve as a neurotransmitter in the commissural path to-area CA1 of the dorsal hippocampus.